Process for the production of toluol



Jan. 8', 1946. V G. E. LIEDHOLM ET AL l 2,392,330

I PROCESS FOR THE PRODUQTIQN OF TOLUOL 2 SheetsL-Sheet 1 Filed June 10,-1940 Fig. I

PokurAqzn Toluo '.Figm

G. E. LIEDHOLM ETAL PROCESS 4FOR THE PRODUCTION OF TOLUO'.'`

Jan. 8, w46;

Filed June l0, 1940 2, Sheets-Sheet: 2

vrlveni'cgr's: Gzorqz Edward Lzdholm v Frank M. McMillan l "PatentedJam8, 1946 UNITED STATES PATENT ori-ICE PROCESS FOR THE PRODUCTION OFTOLUOL George Edward Liedholm, Long Beach, and

, Frank M. McMillan, Berkeley, Calif., assignors to Shell DevelopmentCompany, San Francisco,

Calif., a corporation oi' Delaware Application June l0, 1040, Serial No.339,732

f 'z claims. (ci. 26o-,essi

The'present invention relates to a process for the production of toluolfrom naphthenic distil- Alates. An object of the invention is to providea -method whereby commercial grades of toluol suitable for nitration,solvent use, and the like may be produced in a mosteconomica'l mannerfrom available naphthenic hydrocarbon fractions o1' natural and/orsynthetic origin.

Toluol is one of the-primary compounds upon which aromatic chemistry isbased. It is employed in large quantities as a starting material for thesynthesis of a great variety of useful products such as dyestuils,explosives, drugs, flavors, perfumes, photographic developers, plastics,intermediate chemicals, and many others. Virtually the only source oftoluol is, however, a byproduct from the distillation of coal, beingrecovered in a yield of about 0.00125 %l based on the coal -treated orabout 0.25% based on the coal-tar obtained. Consequently, the supply oftoluol is primarily dependent upon the condition ofthe steel andcoal-tar industry and is in any case limited. Aside from the numeroususes where its application is more or less obligatory, toluol has agreat many potential uses which have been curtailed by its limitedAsupply and relatively high price. As a consequence considerableattention has been given to the possibility oi producing toluol fromother sources. v,

This problem has been considered from two angles. The first of' these isto recover toluol from aromatic petroleum fractions, particularlycracked distillate's. It is known that dlstillates from certainpetroleums and most highly-cracked y distillates contain-appreciablequantities of -aromatic hydrocarbons from which it ispossible to'recover highly aromatic distlllates and even yrelatively pure aromatichydrocarbons by a suitable conrbination of steps involving fractionationand extraction. The recovery oi' ,toluol from such distillates is,however, quite diincult and has not provento -be economical. In the rstplace, only a small proportion of the aromatic hydrocarbons in thesedistillates is: toluol, and consequently, large quantities of materialmust be processed to recover relatively small yields. Furthermore', thetoluol in these distillates, even after a preliminary closefractionation, is present in Aan extremely complicated mixture ofhydrocarbons from which it is most dimcult to separate'a toluoloisatisfactory purity. .Forsome applications, such in particular as itsuse as a solvent, pure toluol is not necessary. For most of itsapplications, however, particularly'where it is used as a startingmaterial in-various chemical syntheses, toluol of at least 98% purity isdemanded. One of the major uses of toluol, for example, is in theproduc-v tion of T. N. T. Toluol for this purpose must be water-white,have al boiling range of not -more 5 than 1 C., and have av 'specificgravity at 15.5/15.5 C. between 0.866 and 0.874. It must further-morepass the standard sulphuric-acid Iwash test which means that it must befree oi.' all but the minutest traces oi' oleiine hydrocarl bons andother impurities whichare normally present in considerable quantities inthe parent petroleum distillate. It is known that during the World WarT. N. T. was produced from relatively impure toluol fractions obtainedfrom petroleum l distillates. This, however, necessitated executing thenitration step-wise with intermediate treatments for the removal oi theimpurities and was `only resorted to due to the emergency at the time.`While toluol of sufficient purity can bel The other approach to theproblem is the syny thesis of toluol from non-aromatic hyrocarbons.

It has long been known that hydroaromatic hydrocarbons may becatalytically dehydrogenated to-aromatic hydrocarbons. Thus, it has beenshown in the laboratory that toluol may be easily produced frommethylcyclohexane by catalytic dehydrogenation. While this. has longIbeen known it has not led to the commercial production of toluol dueprimarily to the lack of a vsuitable source oi methylcyclohexane. It isknown .that certain napththenic distillates contain aD- preciablequantities oi methylcyclohexane. Hereagain, however, the small yieldsand dimculty of separation of` a commercial grade oi' toluolde- 40 tractfrom the practicability of the process.

' Quite recently. it was discovered that cyclic hydrocarbons can beproduced catalytically from catalytically by passing vapors or thehydrocarbon over a cyclization catalyst under appropriate conditionswhereby a. simultaneous dehydrogenation and ring-closure takes place. Itis thus seen that, starting from petroleum, toluol may ll-be potentiallyproduced from three sources: .(a)

recovery of naturally-occurring toluol, (b) formation of toluol frommethylcyclohexane, and

(c) formation of toluol Afrom paramnlc hydrocarbons (n-heptane, 2-methylhexane, and 3- methyl hexane) by cyclization-dehydrogenation.

According" to theprocess of thepresent invention the larger part oi' thetoluol is usually produced by the dehydrogenation of methylcyclohexane.The process, however, does not rely solelyupon the small amount ofmethylcyclohexample:

. By weight Aromatic hydrocarbons 1-10 Naphthenic hydrocarbons 15-75Paraflln hydrocarbons 25-85 ane occurring naturally in the hydrocarbonfeed.

Additional amounts of this hydrocarbon are produced in the process fromthe other hydrocarbons. I'he process is also adapted to recoversubstantially all of any toluol naturally present in the feed. Moreover,the process is adapted to allow `the production of additional amounts oftoluol by catalytic cyclization. As a result, the process of ourinvention is unique in the exceptionally high yields of toluol obtained.

According to the process of the invention, we

i produce toluol Virom naphthenic distillates. By

' in the molecule.

naphthenic distillates w e mean hydrocarbon distillates of natural or`synthetic origin, containing an appreciable quantity of naphthenic andparamnic hydrocarbons having seven carbon atoms are obtained from 'alarge number of crude petroleums. A few typical crudes from whichsuitable naphthenic distillates may be obtained are, for example. LosAngeles Basin crude. Huntington Beach crude'. Dominguez Hill crude,Vensuch fractions.

tura crude and El Capitan crude. The naphthenic distillate is preferablyfractionated to separate a narrow cut containing the larger part of thehydrocarbons having seven carbon atoms in the molecule. Such a fractionmay, for example, boil between bout 190 F. to 230 F. The

boiling points of th se convertible paramn hydrocarbons are:

. v F. Normal heptane 209.2 .it-methylhexane 194 3-methylhexane 197.3

This fraction. if from a naphthenic distillate, a1so .containssubstantially all of the methylcyclohexane (boiling point 213 F.)present. These naphthenic distillates also usually contain a small butsignificant amount of toluol. Any toluol naturally present in thedistillate is also included in The advantages of the use of. such afraction are fourfold. First, the fraction representsa practicalproportion of the material to be treated. Second, whenl the fraction issub-- jected to an appropriate dehydrogenation-cyclization treatmenttoluol is produced both by dehydrogenation of the methylcyclohexane aswell as cyclization of thev open-chain paraillns, and

`considerably increased yields are produced.

Thirdfany toluol naturally present in the distillate is recovered.Fourth, the proportion of Suitable naphthenic distillates toluol in theproduct from the dehydrogenationcyclization treatment being larger, thedifficulties and expense of recovering the toluol are reduced.

A suitable method for the separation of such a l fraction is illustratedinthe attached Figure 1.

Referring to Figure 1, it is seen that the naphthenic oil is fed to astill wherein all material quantity of this fraction will varyvaccording to s the character of the distillate. but in most casesboiling below the initial boiling point of the deth'iesiied fraction istaken oif overhead. The

--'sired ffraction is removed overhead. The bot- L toms-f-romthis stillpass to a second still wherein 'following example:

will be a sizablefraction. @Typical analyses of these fractions fromsuch crudes-are for ex- It is not practical, however, to produce toluoldirectly from -suchnaphthenic fractions.. This is due primarily to thefact that @when subjecting such commercial fractions to a catalytic dehydrogenation-cyclization treatment the active life of the catalyst isvery short. This requires vfrequent stopping of the reaction andreactivation of the catalyst. The reactivation treatment.

which is effectedb'y carefully burning deposited carbonaceous materialfrom the *catalyst under controlled conditions, greatly decreases theeconomy of the process since it.' is time-consuming, causes loss ofmaterial, causes a gradual'perma- ,nent loss of the catalyst activity,and requires the handling of large quantities of reactivating andflushing gases. .The results obtained upon subjecting such fractions toa conventional dehydrogenation treatment are illustrated. by the ExampleI A straight run naphthenic gasolinewa's fracl tionated to prepare a19o-230 F. heart cut. A

detailed investigation of its composition showed thatA it contained- C1components in the following volume ratios:

l This material was subjected tol s catalyticdehydrogenation-cyclization treatment under the following conditions: A

Catalyst=chromium oxide *supportedfupon activated alumina (l1 Cr)Temperature=975 F. l. Time=6 hours `Space velocity=0.73 vol. liquid/vol.catalyst/hour Pressure==15vlbs./sq. in. exit pressure vPure n-heptane,or pure methylcyclohexane, 'orI a synthetic mixture of pure n-heptaneand pure methyl' cyclohexane, whenv heated under these conditions, give'excellent yields of' toluol with little formation of carbon and gas. Theabove fraction, however,.ail`orded a conversion to tol- .uolof onlyabout 7% to 10% (i. e. 15% to 17% toluol in the product). Moreover, thecarbon- -aceous material deposited on -the catalyst amounted to 4.6% .byweight oi' the feedtreated, and, approximately l13% by weight of thefeed was converted' to gases. Under optimum conditions it required about4i hours to regenerate the catalyst.

vAccording to the process of the present invention, not only are theyields of toluol obtained from any given naphthenic distillate muchgreater, but the decline in the catalytic activity of the catalyst ismuch slower and less time is required. for regeneration, and a crudetoluol is produced from vwhich commercial grades lof to1- uol may berecovered more economically. f

It is found that the above-described fractions 1l ,i'rom naphthenicdistillates invariably contain considerable quantities of alkylatedcyclopentanes, such in particular as:

Boiling point, F.

Other hydrocarbons Which are usually found to be present to variousextents, include:

' Boiling point, F. 3,3-dimethylpentane 186.8 2,3-dimethyipentane 193.5.'i-ethylpentane 199.9 Propylcyclobutane 210.2-212 2,2,4trimethylpentane210.7

These latter hydrocarbons when present act primarily as inert diluentsand are only detrimental insofar as they make the recovery of the toluolmore diflicult. The above-mentioned alkyl-cyciopentanes, on the otherhand, are found to be very detrimental. When present, even in quitesmall quantities in the hydrocarbon fraction to be treated, they causea. rapid deterioration of the activity of the catalyst. It is found thatif these detrimental alkylcyclopentanes are removed, 'the active life ofthe 'dehydrogenationcyclization catalyst is greatly improved, much lessfrequent reactivation of the catalyst is required, and the process ismade much more economical. According to the process of the presentinvention, these detrimental-acting dimethyl' cyclopentanes are not onlyremoved from the hydrocarbon fractions to be treated, but they areconverted into toluol, thus materially increasing the yield. "Theremoval of these poisoning dimethylcyclopentanes is effected bysubjecting them to a suitable isomerization treatment whereby theyareconverted to a large extent to I methylcylohexane. 1

If a hydrocarbon fraction from a naphthenic distillate, boiling forexample between 190 F. and 215 F., is subjected to an isomerizationtreatment, it is found that a certain improvement in the yield andeconomy of the process results. Far greater improvements may beobtained, however, if the hydrocarbon fraction is rst separated into twofractions, one containing the larger part of the normal heptane andmethylcyclohexane and the other containing the larger part of thedimethylcyclopentanes and the methyl hexanes, and subjecting to theisomerization treatment only the latter. There are several reasons, wehave found, why this method .is superior. By separating the hydrocarbonto be treated into two such fractions, forv example boiling between 200F. -to 230 F. and 190 F. to 200 F. respectively, the amount of materialto beprocessed by into a lower and a higher boiling fraction as demakesit 'possible to recover toluol of excellent purity in an economicalmanner.

The process of our invention, then, in its more general aspect comprisesseparating a naphthenic f distillate to lbe treated into two fractions,subjecting the lower-boiling 'fraction to an isomerization treatment,subjecting the fractions to a dehydrogenation-cyclizationA treatment,and recovering toluol from the thus-treated product. This is illustrateddiagrammatically in the attached ow diagram, Figure 1. The narrow C-'Icut from the naphthenic distillate is separated scribed above. Thus, inthe attached iiow diagram the desired fraction to be treated is passedto a third still wherein it is separated into a lower and a higherboiling fraction. While in the above w have explained the process interms of two separate distillations, i. e. first separating a C-'l cut,boiling for example between 190 to 230 F., and vlater separating this.fraction into a higher and lower boilingfraction, it is of courseobvious that the same result may be obtained directly by separating twocuts of suitable boiling range. Very suitable boiling ranges forthesefractions are, for example, 190 to 200 F. and 200 F. to 230 F.respectively. This separation `may likewise be eiected by any of theconventional ywhich increase the .amount of the material to be processedand make the separation of a pure toluol more dilcult. On the otherhand, if the initialboiling point is chosen much above 190 F., a loss intoluol yield results.` In general,

the initial boiling point of the lower-boiling fraction is chosen atabout 190 F., for example 180 to 195 F. The upper range of boiling pointof the higher-boiling fraction is preferably chosen somewhat about 210F., for -example 214' to 240 F. Although higher-boiling material may beincluded in the fraction, its presence isin general undesirable since itmakes the recovery of pure toluol more diiilcult.

According to the present process the lower'boiling of these twofractionsis subjected to an isomerization treatment. This may be effected bycontacting the fraction in the liquid or vapor phase, preferably in'theliquid phase, under suitable conditions w-ith an isomerization catalyst,a hydrogen halide promoter, and, if desired, hydrogen. Preferableisomerization catalysts are those comprising anhydrous aluminum chlorideand/0r aluminum bromide. Of these, aluminum chloride is preferred sinceit is less expensive, easier to employ and has much less tendency thanaluminum bromide to cause degradation of the naphthenic hydrocarbons.Other acid-.acting catalysts of the Friedel-Crafts type such as thehalides of. Zr, Zn, Sn, Be, Nb, Ta, Sb, B, Cu -and Cd may also beemployed if desired in conjuncmuch more eillcient elimination ofhydrocarbon types not directly convertible to toluol bycyclization-dehydrogenation, this method of operation also materiallydecreases the difficulty and the expense ofthe subsequent toluolrecovery and tion with the aluminum chloride. The catalyst may, ifdesired, be employed as a solid either in suspension inthe liquidreaction mixture orfas a xed bed. In the latter case it is preferablyem.

ployeds lumps, granules or pellets ,of suitable size, preferablydeposited upon or mixed with a suitable solid support. catalysts areproduced when aluminum chloride Particularly effective- A 2,892, issupported upon or intimately mixed with one of 'the various preferablyadsorptive siliceous and/or aluminous materials ot natural or syntheticorigin which contain an appreciable amount of rmly-bound water. Suitablemateriais of this category are, for example, thenaturally-occurringminerals and clays such as pipe pump 3 via a line 3. A portion ofthepartiallyspent liquid catalyst may be continuously or in termittentlyremoved if desired v'ia valved outlet 9 and an equivalent amount oi'fresh catalyst may be added via pipe I0. The hydrocarbon from separator1 is passed through a cooler I I and filter I2 to remove any globules ofsuspended clay, bauxite, fuliers earth, bentonite. Florida earth,meerschaum, kaolin, iniusorial earth,

kieselguhr, diatomaceous earth and the like; the' various treated'claysand' clay-like materials: and

artificially prepared materials such as Activated- Alumina, silica gel,the artiilcial permutltes and the like. These materials are preferablyheated in a dry atmosphere at a moderately elevated temperature, such,for instance. as about 200 to 300 C., until they substantially cease togive oft water. Although these materials produce Apreferred catalystswhen combined with aluminum chloride, other supporting materials such asactivated carbon, coke, -crushed brick, pumice and the like may also beused.

While solid catalysts may be suitably employed we have developed animproved and advanta- "1 geous method whereby the isomerizationtreatment may be effected in a continuous manner using liquid catalysts.Particularly suitable liquid catalysts are those of the Gustavson (C.190311 1113) and Ansolvo (German Patent No. 535,473) acid types whereinaluminum chloride is in combination with various organic compounds suchas organic acids, ethers, esters, hydrocarbons, etc.,

catalysts and is then passedto tank I3.

The assembly of apparatus illustrated diagrammatically in Figure II isadapted for the use oi' liquid catalysts of the above-mentionedGustavson or Ansolvo acid types. The catalyst may be prepared in anyconventional manner and supplied to the system, for instance,via lineI3. For the sake of completeness provision is also made for thepreparation oi the catalyst in the iiow diagram of Figure II. Thisapparatus, which may be considerably modiiied if desired, comprises amixing vessel I4 interconnected in a circulatory system via circulatingpump I5 to a-small chamber I 0. Aluminum chloride or other catalysts arecharged to the mixing vessel I 4 and a quantity ofthe organic materialto be reacted therewith to form the complex catalyst is introduced vvlaline I1. This may be any o e or a mixture of a great number of organicco pounds. In case the complex catalyst is one of Ill) and those of themetal double-salt type in which the aluminum chloride is in loosecombination' with similar metal halides such, for instance, as I thehalides or Sb, Sn, Zr, Cu, Ti, Na, K, Li and the like. By employingaluminum chloride in combination with certain of these metal halides,excellent isomerization catalysts may be prepared which melt toiree-ilowing liquids at very moderate temperatures and may be pumpedthrough the reaction system with or countercurrent to the hydrocarbonfraction to be isomerized. The use of liquid catalysts Vin theisomerization' has denite advantages. The naphthenic distillates to betreated often contain small amounts of aromatic and/or olenichydrocarbons. 'I'hese hydrocarbon types, if present, are

generally quite detrimental when employing nxed f beds of catalysts.When employing iiuid catalysts; hydrocarbon fractions containing smallamounts .of'oleilnes and/or aromatic hydrocarbons may be treated withoutdifficulty. These liquid catalysts moreover havef aconslderably milderaction and in general are much less prone to cause degradation of thenaphthenic hydrocarbons. Also, they allow the isomerization Yto beeffected'in simple apparatus in a continuous most practical manner. Aflow diagram of a suitable isomerization'. unit employing this principleis' illustrated in the attached Figure II. Referring to Figure I I, thehydrocarbon to be treated is fed from a storage tank I via pump 2 to acirculating pump 3 wherein it is mixed with a liquid catalyst andpromoter and circulated through a heater l and time tank 5, and back tothe circulating pump 3 via a valved line 3. .The time tank 5 ispreferably equipped with perforated lbailles or other means to insurethorough contact with the hydrocarbon and liquid catalyst. All or aportion of the material passing through 'time tank 5 is withdrawn to aseparating device I Vwherein the liquid catalyst is separated from the-bulk of the hydrocarbon. The liquid catalystfrom separator 1 isrecycled to the .circulating the Gustavson type (C. 1903 II 1113) theliquid added may be an aromatic hydrocarbon or a hydrocarbon mixturerich in aromatic hydrocarbons. Aromatic hydrocarbons, a's a class, aregenerally suitable. Thus, for example, benzol and the variousalkylderivatives thereof'may be used. Particularly suitable catalysts ofthis type may be prepared from the so-called bright-stqpks or Edeleanuextracts obtained by the extraction of aromatic-containing distillateswith sulphur dioxide. These catalysts are found to contain approximatelytwice as much aluminum chloride, for example, as catalysts of the samegeneral type prepared from benzol or toluol. .They therefore have a muchlonger life. Catalysts of this Vtype are described in United StatesPatents Nos. 1,671,517, 1,586,857 1,999,345, and British Patent No.7,112- (1914). Aromatic extracts obtainee-- by extraction with otherselective solventsfmay oi course, likewise be employed.

The isomerization treatment is preferably Tex; .Q

vapor of at least 1 to 3 atmospheres) is employed v and the hydrogenchloride is recycled through the reaction zone. Thus, in Figure 1I theproduct from tank I3 is forced 'via pump I3 to a stripping column I3wherein the HCl promoter and any other lower-boiling material 'is takenoir overhead. ,The overhead fraction is passed through a vcooler 20 intoa vessel 2|. Condensed liquid in vessel 2| is pumped back to thestripping tower to serve as reilux. The bottom product from tower I3 ispassed through a caustic scrubber. 22-

to remove any last traces of promoter and is then Stored in tank 23.'I'he hydrogen chloride promoter separated from the product in thestripping column is recycled back tothe isomerization system 4via line23; The hydrogen halide (and vement 'sourcegsuclrasa' high-pressurecylinder 'liquidfcatalysts'the i'somerizaton. processy mayk be executedwith onlyiv'ery smallgamounts'of adi-ogen chloride promoterffo'r j 1%.VInfsuch-caseS.it -mayb more-economical 'no tto j attemptjto recover andrecycle the 'proi moterl. "Inthis-caseL-thejproduct fromtank I3 maybesimply' caustic-washed-andsent to stor` age. Insteadoffeeding.inzhydrogenhalide per .se, the hydrogen chloride or. otherhydrogen halide promoter may be carried to the,- reaction drogen halidesuch as Aarid the like.

found that the isomerization is accompanied 'by ment with a continuouslyrecirculated liquid catalyst under the following conditions:

' Temperature-T475* F. Pressure=48 lbs/sq. in.

"I'lie catalyst was prepared by combining technitaining a suitabledrying agent such as CaClz, P20, activated-alumina, ori the like.y Smallamounts of excess gas may be. vented from time to time by valvedoutlet/.11. Make-up hydrogen' chlorideis supplied .tothe-system from anycon- 24.' pointed'iout above,.however, when using tance; :less than,

zone, dissolvedl in one of Vthe reactants, or. mayv be generatedin.therea'cti onzone. from added materials which under the reactionconditions reactor. decomposeto liberate hydrogen-halide.;

inorganic {salts containingmolecularly-boui'id *hy- Pbsoi-zHcLoosoiznclThe isomerization may effectedover a wide range of temperaturesdepending upon the space especially when the catalyst is particularlyactive o orthe temperature is somewhat high,"it maybe appreciableamounts of side reactions. This may be easily remedied if it'oocurs byA.Slightly decreas-.. ing the. temperature or concentration ofv pro-f.45 moter, `or if desired, byf effecting. the fisomeriza' the 'use ofhydrogen is not generally necessary, provision for its use is shown inFigure II. Thus, if hydrogen is recycled along with the promoter,make-up hydrogen may be added from cylinder 25. f

I'he isomerization, of naphthenic fractions, -aocording to theabove-described method, is.i11u s trated'ir'i the following. examples;l'

. Bemelen# 1 y A C-'7 fraction such as described above' wasseparatedinto two fractions, the lower of 'which boiled betvveeiilBZ.and 204 F. This narrow fraction was subjected to an isomerization treat-HC1 promoter=5.2% by weight (recycled) Ratio of liquid catalyst tohydrocarbon circu- -lated=0;'l7.

Contact time=1.7,5hours cal aluminum chloride with about 0.6 pm by temis preferably passed through a drier 2.6 convthe isomerization', 39 %(or839' of 25; Pressure:loulnsysqrin. ana isllis/sq in 'Contacttime=15jmiiiutes Stir`iing=`150 R. Rflilluy 'I'hist'reatmentwas carriedout for 172 hours with the'same'catalyst without ny noticeable declinevelocity, concentration ofbr'omoter emplfiyedand il'. m 'the' catalymcmuy an with an upon the activity'of the catalyst'.l 'A1t hought`em.`

i peratures ranging'from about room ,temperature 11D t0 about. 400 FLn'lay befemployedfthe' isom- "J erizationmaybe eifectedfeconomically atquite Ymoderate temfleraf.`tures'' such,v for example, as

'from about 100 F. to 200 F." In some cases,

Ratio` of, liquid-catalyst'-tohydr ibnfreircu Contact time=f1f5'minutes'.

'f "Thefconversionto methylcycloheiiane"'was'f78%. l

vEglantine 1V j The.mplithenlc duction of methyleyclohexane of 34%.

formed in the'treatment .by traces of siclel reactions such as,polymerizatiom alkylatlon', -etc.

and/orA any lower-boiling unisomerlzedlmaterial.

The amount of' products of side reaction's'is usu.

4ally small andthe extra fractionation step may often be omitted withoutill effects.; According to la .preferred embodiment of the invention,the

y beiieii'tl o f .the subsequent fractionation to remove unisomerizedmaterial aszwellas any higherboiling productsis realizedlwithout thenecessity loft providing separate fractionatingcolumns. by

. blending back the isomerized productfiis'omervate) with the napnthenichydrocarbn'feed. Thus, the isomerisate maybe blended with the feed tothe rst, second,.or third fractionatingl column illustrated in Figure.I. This also has' the advantage of causing any unconverted material fromthe isomeriz'ation step to be recycled through thatv step. In' .the flowdiagram of Figure I tnis optional 'recyclegand fractionation step isindi- 'cated immediately following. -theisoin'erization stepin brokenlines.

The lower-boiling vfractioiir'after bengfsub@ .v jected to theisomerization'treatinent, 'adthe above-described higher-boiling.fraction arefthen subjected to tli'e dehydrogenation-cyclizationtreatment in the usual manner. This may be most practically eected inone vapparatus employing the "recombined fractions, but it may also beeifected separately with each fraction if, for any reason, this isdesired. 'I'he dehydrogenationv treatment may be effected by any of theconventional methods, using any of the conven' tional dehydrogenationand/or .cyclization cata lysts.l `In general, however, `thedehydrogenationcyclization treatment .is .effected by passingthe lvap`ors of the hydrocarbon a reaction saaawywdeath@ hydrocarbon fractiondescribed u in Example II was isomerized using the same cat.

alyst in a stirring autoclave under tli'e following- .condtmin' I zonecontaining a bed of catalyst and maintained under suitable reactionconditions. The optimum reaction conditions depend upon the catalystein-.- ployed and may vary considerably. In some eases, for example,such as when employing a catalyst composed of nickel and tungstensuliides,

via line B.v The toluol fraction from column 55,

` after passing through the' cooler 51 and collector f 58, is pumped viapump 59 and line 60 to a column the reaction is preferably executedunder a considerable hydrogen pressure, for example, from 20 to 100atmospheres; Inother cases, for example, when employing a catalystcomprising an oxide o f a metal of the 4th, 5th orth group of theperiodcsystem, the process is preferably executed under about atmosphericpressure.. for

example,V from 1 to 4 atmospheres, lwith a mol ratio of hydrogen rangingfrom 0 up to about 8,

depending upon the temperature activity ofthe catalyst, -space velocity.etc. Likewise, the tem' peraturelmay vary considerably. Temperatures .Inmany cases it is of sufcient purity to be used without furtherpurification as a solvent and the like where a toluol of high'purity isnot required.

An advantage of the present process is that the toluol may be recoveredfrom the product in almost any desired degree of purity by relativelysimple methods and with greater eiiiciency and Thus, itis generallypossible 'to produce almost a complete yield 'of toluolmeeting thestringentrequirements for nitration by a simple extractive distillation.In/some cases a wash with dilute sulphuric acid may be`required.

'I'he recovery, of toluol of the desired purity may be` .eiected by anyone "or combination `of conventional methods such as fractionaldistillation, azeotropic distillation, solvent extraction, extrac- -tivedistillation, crystallization, or the like. Ex-v tractive distillation,being both'highly effective economy. This' is due largely to the factthat a considerable proportion of the contaminating limpurities havebeenconverted into toluol.

l:economical operation under certain stances, will at once be apparentto those skilled 6I adapted for extractive distillation. A suitablepolar agent is fed at a suitable point near the top of the column inregulated quantity via pipe 62 and automatic control means 63. The polaragent employed in the'extractive distillation may be any one of the manypolar solvents having a preferential solubility for toluol andpreferably -having ab'oiling point of at least 220 F. Particularlysuitable polar agents for this purpose are crcsylic acidl and otherhigher-boiling .alkyl phenols, anilin, furfural, carbitol, antimonytrichloride, and thelike. Hydrocarbon impurities -are removed overheadfrom column 6i .via pipe 66. -The bottom product from column 6Icontaining the toluol and the polar agent is then fed toya fractionatingor stripping column 65 wherein the toluol is separated from the polaragent. Substantially pure toluol is removed overhead via cooler'BG,collector 61, andisled to storage or to a dilute acidtreatment via pipe68. The polar agent is recovered as a bottomproduct via pipe 59. It maybe sent to storage andre-used in column 6|. Further detailsregarding'extractive distillation may be found in French Patent No.815.302. f

In the foregoing we have explained our invention in considerable detailindicating various pre- -ferred embodiments as well ascertain-modifications thereof. Numerous other suitable modica.- tions,many of which may aiord slightly more circumin the art. It is thereforeto be understood that theinvention is not limited to the exact form orand economical, is a preferred method. A suitable recovery unitemploying cxtractive distillation is illustrated in the now diagram ofFigure III. Referring to 'Figure III, the toluol-containing materialfrom the dehydrogenation unit is fed to -a fractionating-column 5|,provided with con- '1 denser 52, collector 53, and means 54 forreturning' a part of the overhead material to establish reiiux.Fractionating column 5| is adjusted to remove the greater part of thenon-converted and lighter-boiling hydrocarbons. This lighter loverheadfraction may be disposed of -for other purposes such as motor fuelormai?. depending upon its composition, be recycled. If it consistslargely of open-chain -paramns including normal heptane, it may berecycled through the dehydrogenation-.cyclization If. as is sometimesthe case, .it also contains any appreciable quantities of .alkylcyclopentanes, it is preferably recycled through-the isomerizationtreatment. The rein flow diagram Figure I in broken lines. The bottomvproduct from fractionating` column 5I l may be subjected. directly tothe extractiva distilv lation treatment. However, it is often advisable05\ realizing maximum catalytic yelilciency which cycling of thismaterial being optional is indicated to first remove a relatively puretoluol fraction in a second-fractionating column 55. The bottom productfrom column 55 consists of small amounts forms -described and that allsuch modifications as fall within the spirit'of the invention areintended to be embraced in the language'of the accompanying claims.

`We claim as our invention:

1. In a process for the production of toluol from` naphthenic straightrun gasolinesvia catalytic dehydrogenation, the method of producingincreased yields of substantially pure toluol while realizing maximumcatalytic efliciency which comprises separating from a naphthenicstraight run gasoline by fractional distillation a fraction boilingbetween about F. and about 230 F..

separating said 190 F. to 230 F. fraction intotwo fractions boilingbetween about 190 F. and

about 200 F and between about 200 F. and about 230 F. by fractionaldistillation, contacting the 190 F. to `200 F. fraction with an aluminumchloride catalyst under isomerization conditions, subjecting the.190 F.to 200 F. fraction together with the` 200 F. to 2305 F. fraction to acatalytic dehydrogenatiom and recovering substantially pure toluol fromthe product.

2. In a process for the production of toluol from naphthenic straightrun gasolines via 'catalytic ,dehydrogenatiom the method of producingincreased yields of substantiallypure toluol while comprises separatingfrom the naphthenic straight run gasoline byfr'actional distillation afraction'boilingbetween abcut 190 F. and'about f 230 F., separating said190". F.- to 230 F. fraction into two fractions boiling between about?1901'F. and about 200 F. and between abOllt 200"I F. and about 230 F. byfractional distillation', contacting the 190 F. 'to 200 F..fract'ionvWitha liquid aluminum chloride complexcatalyst underisomerlaationVconditions, subjecting tbe 19o' 11". to zoo' F. fraction together withthe 200 F. to 230 F. fraction to a catalytic de.

hydrogenation, and recovering substantially pure toluol from theproduct. V

3. In a process .for the production of toluol from naphthenic straightrun gasolines via catalytic dehydrogenation', the method of producingincreased yields of substantially pure toluol while realizing maximumcatalytic eillciency which comprises separating from a naphthenicstraight run gasoline by fractional distillation a fraction honingbetween about' 190 F. and about 230 F., separating said 190 F. to 230 F.fraction into two fractions boiling between about 190 F. and about 200F. and between about 200 F. and about 230 F. by` fractionaldistillation, contacting the 190 F. to 200 F. fraction underisomerization conditions with a liquid catalyst prepared by combininganhydrous aluminum chloride with an aromatic kerosene extract,subjecting the 190 F, to 200 F.

fraction together with the 200 F. to 230, F. fraction to a. catalyticdehydrogenation, and recovering substantially pure toluol from theproduct.

4. In a process for the production of toluol from naphthenic straightrun gasolines via catalytic dehydrogenation, the method of producingincreased yields oi.' substantially pure toluol while realizing maximumcatalytic efficiency which comprises separating from a naphthenicstraight run gasoline by fractional distillation a fraction boilingbetween about 190 F. and about 230 F.,

separating -said 190" F. to 230 F. fraction into two fractions boilingbetween about 190 F. and

about 200 F. and between about 200 F. and

about 2306 F. by fractional distillation, oontaet-` ing the 190 F. to200 F. fraction with an aluminum chloride catalyst under isomerizationconditions, fractionally distilling saidv isomerized fraction to'removematerial boiling below about 200 F., subjecting the residual isomerizedfraction together with the 200 F. to 230 F. fraction to a catalyticdehydrogenation,.V and recovering substantially pure toluol from theproduct.

5. In a processdor the production of toluol from naphthenic straight rungasolines-via catalytic dehydogenation, the method of producingincreased yields of substantially pure toluol while realizing maximumcatalytic eillciency which comprises separating from a\naphthenicstraight run gasoline by fractional distillation a fraction fromnaphthenic straight rune gasolines via catalytic' dehydrogenation, themethod of producing increased yields of substantially pure toluol'whilerealizing maximum catalytic efilciency which comprises separating'from anaphthenic straight run gasoline by fractional distillationa fractionboiling between about 190 F. and about 230 F., separating said 190 F. to230 F. fraction into two fractions Kboiling between about 190 F.and-about 200 F. and between about 200. F. and about 230 F. byfractional distillation, contacting the 190 F. to 200 F. fraction withan aluminum chloride catalyst under isomerization conditions, subjectingthe 190 F. to 200 F. fraction 'together with the 200 F. to 230 F.fraction to a catalytic dehydrogenation, and recovering substantiallypure toluol from the product by extractive dis'- tillation. i

'l'. In a process for the production of toluol V from naphthenicstraight run gasolines via catalytic dehydrogenation, the method ofproducing increased yields of substantially pure toluol while realizingmaximum 'catalytic eillciency which comprises separating from anaphthenic straight run gasoline by fractional distillation a lfractionboiling between about F. and about 230 F., separating said 190 F. to 230F. fraction into two fractionsboiling between about 190 F. and

` about 200 F. and between about 200 F. and about 230 F. by fractionaldistillation, contacting the `190 F. to 200 F. fraction with yanaluminum chloride catalyst under isomerization' conditions, subjectingthe 190 F. to 200 F. fraction together with the 200 F. to 230 F.fraction to a catalytic boiling between about 190 F. and about 230 F.. A

dehydrogenation with a chromium oxide catalyst,

and recovering substantially pure toluol from the product. fr

GEORGE EDWARD LIEDHOLM.`

.FRANK M. MCMILLAN.

